The present invention relates to optical channel monitoring devices and systems. Optical channel monitoring is increasingly being used by telecommunications carriers and multi-service operators. Optical channel monitoring is particularly important for modern optical networks that use reconfigurable and self-managed fiber-optic networks.
For example, reconfigurable add/drop multiplexers (ROADM) require an optical channel monitor. In ROADM systems, a dense wavelength division multiplexer (DWDM) channel monitor provides an inventory of incoming wavelengths to avoid “wavelength collision” with added channels, as well as an inventory of outgoing channels when the ROADM is used for multi-degree ring-to-ring switching applications. The DWDM channel monitor is also relied on to provide channel-power information to variable optical attenuator (VOA) control electronics so that added channels can be equalized with the pass-through channels.
Optical channel monitors are also needed for multi-haul fiber-optic transmission systems. Multi-haul fiber-optic transmission systems include dynamic components for automatic span configuration at setup and for self-adjustment over time to compensate for changing environmental conditions. These dynamic components usually require feedback from an optical channel monitor. Systems with such dynamic components using feedback from an optical channel monitor enable system designers to maintain tight system margins.
State-of-the-art multihaul system designs often have DWDM channel monitors, which effectively build more intelligence in the optical node. These multi-haul systems can be self-managed optical nodes that adjust for changing environmental and input conditions. Such multi-haul systems allows for automatic testing and regression-testing in various network configurations. It is anticipated that future optical networks will include sophisticated distributed intelligence that will require more embedded DWDM channel monitoring in every optical node and eventually in every optical sub-module.
Furthermore, as the number of wavelengths in an optical network increase, so does the regenerator cost as a percentage of the total DWDM system cost. Carriers are currently requiring equipment vendors to devise ways to reduce the number of regenerators. One way of eliminating regenerators in DWDM systems is to require the client line cards (for example on routers) to source long-reach DWDM channels instead of short-reach 1310 nm channels. However, removing regenerators on DWDM systems also removes the SONET/SDH monitoring capability at that network node. In such systems, DWDM channel monitors can be used for monitoring functions because they provide DWDM channel visibility regardless of the native modulation format for each DWDM wavelength.
Thus, optical channel monitors can be used to provide higher network reliability and more efficient operation, administration and provisioning. Therefore, using optical channel monitors can significantly reduce the OpEx costs for many carriers and network service providers.